The level of magnetically recorded audio, video or data signals is known to differ if record current levels vary during recording processes on tapes using different recorders, or when recording on different tapes. More particularly, even with the same record current, the recording levels may vary due to the different properties or characteristics which exist between, for example, different heads, tapes and environments. To exemplify, differences in the magnetic properties of tape materials can cause variations in the levels of magnetically recorded signals in different tapes even though the record current is constant. Variations in the recorded signal levels, in turn, cause problems such as poor edit overwrite and poor interchangeability of tapes between recorders. Thus, it has always been highly desirable to optimize the record current when recording audio, video or data signals on tape, to provide consistent recording levels in all tapes using any recorder/reproducer apparatus.
Typical of present techniques for setting the record current for a record head when recording a tape in a magnetic tape recorder, particularly those with ferrite heads, is to use trial and error while in the record process until the saturation level of the tape is found. In some prior techniques, a previously stored fixed "reference" value is used to set the record current for the record head, generally by manually adjusting the record current until the required rf playback amplitude is achieved. Such techniques fail to eliminate the very substantial playback head changes in efficiency which occur during the life of the head, and fail to account for tape-to-tape output level variations. Such techniques have been utilized not only in present digital video tape recorders, but also, in setting the record currents in type-C analog video tape recorders.
However a problem arises when using the Nyquist frequency and saturating the tape. That is, even if the Nyquist frequency is recorded on tape, and the record current is adjusted until the tape saturates, it is impossible to ascertain how deeply the lower frequency levels, such as 1/3 Nyquist, are recorded on the tape. However, it is these frequencies in the lower half of the video signal frequency spectrum, which generally cause recording at prohibitively varied and high levels. This condition also exists in an audio system where the different frequencies of the audio signal frequency spectrum require varied recording levels. In turn, where a recording is made at high levels and an insert edit with no prior erasure subsequently is performed over the recording, the high level lower frequencies of the old recording are not erased by the new edit recording. This results in a very poor overwrite condition and an unacceptable insert edit.
Thus, it is highly desirable that recording of audio, video or data signals be done uniformly at all times and without incurring prohibitively high or varied levels of recording on tape, which would lead to the poor overwrite conditions during editing procedures. In addition, it is highly desirable to maintain the interchangeability of tapes between recorders. However, if the recording level varies, as when using non-uniform record currents or different magnetic tapes, or when the recording characteristics change as the head wears down, then the same record current may provide more or less output, causing a variation in the recording level. This, in turn, also negatively affects the interchangeability of tapes between recorders.